The ability of an organism to regulate the expression of its genes is of central importance. A breakdown in this homeostasis leads to disease states such as, for example, cancer, where a cell multiplies uncontrollably to the detriment of the organism. The general mechanisms utilized by organisms to maintain this gene expression homeostasis are the focus of intense scientific study.
Some cells are able to down-regulate their gene expression through certain ribonucleic acid (RNA) molecules. Namely, RNA molecules can act as potent gene expression regulators either by inducing messenger RNA (mRNA) degradation or by inhibiting translation. This activity is summarily referred to as post-transcriptional gene silencing (PTGS). An alternative name by which it is also known is RNA interference (RNAi). PTGS/RNAi has been found to function as a mediator of resistance to endogenous and exogenous pathogenic nucleic acid sequences, as well as a regulator of the expression of genes inside cells.
Early studies suggested only a limited role for RNAi, that of a defense mechanism against pathogens. However, the subsequent discovery of many endogenously-encoded microRNAs pointed towards the possibility of this being a more general, in nature, control mechanism. Recent evidence has led to conjecture that a wider spectrum of biological processes is affected by RNAi, thus extending the range of this presumed control layer.
A better understanding of the mechanism of the RNA interference process would benefit drug design, the fight against disease and the understanding of host defense mechanisms, among other things.